U.S. patent number 10,241,004 [Application Number 15/841,052] was granted by the patent office on 2019-03-26 for system and method for monitoring the structural health of coupled bearings.
This patent grant is currently assigned to ACELLENT TECHNOLOGIES, INC.. The grantee listed for this patent is ACELLENT TECHNOLOGIES, INC.. Invention is credited to Jeffrey Dean Bergman, Fu-Kuo Chang, Howard Hungchi Chung, Roger Huang, Irene Li, Patrick Joseph Pollock.
![](/patent/grant/10241004/US10241004-20190326-D00000.png)
![](/patent/grant/10241004/US10241004-20190326-D00001.png)
![](/patent/grant/10241004/US10241004-20190326-D00002.png)
![](/patent/grant/10241004/US10241004-20190326-D00003.png)
![](/patent/grant/10241004/US10241004-20190326-D00004.png)
United States Patent |
10,241,004 |
Pollock , et al. |
March 26, 2019 |
System and method for monitoring the structural health of coupled
bearings
Abstract
Placement of structural health monitoring sensors within a
coupled bearing assembly. An exemplary structural health monitoring
system comprises first and second bearings configured for rotatable
positioning along a structure, and a spacer positioned between the
first and second bearings. The first and second bearings are placed
against opposing sides of the spacer, and have a preload force
engaging the respective first and second bearings against the
opposing sides of the spacer. A plurality of sensors are coupled to
the spacer so as to be positioned between the spacer and at least
one of the first and second bearings, the sensors further coupled
to at least one of the first and second bearings so as to be
configured to monitor a structural health of the at least one of
the first and second bearings.
Inventors: |
Pollock; Patrick Joseph
(Oakland, CA), Chung; Howard Hungchi (San Jose, CA),
Huang; Roger (Mountain View, CA), Chang; Fu-Kuo
(Stanford, CA), Li; Irene (Stanford, CA), Bergman;
Jeffrey Dean (Santa Clara, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
ACELLENT TECHNOLOGIES, INC. |
Sunnyvale |
CA |
US |
|
|
Assignee: |
ACELLENT TECHNOLOGIES, INC.
(Sunnyvale, CA)
|
Family
ID: |
50545682 |
Appl.
No.: |
15/841,052 |
Filed: |
December 13, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20180128711 A1 |
May 10, 2018 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
14064019 |
Oct 25, 2013 |
9927323 |
|
|
|
61719332 |
Oct 26, 2012 |
|
|
|
|
61719339 |
Oct 26, 2012 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01M
13/045 (20130101) |
Current International
Class: |
G01M
13/04 (20060101); G01M 13/045 (20190101) |
Field of
Search: |
;73/593 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Le; Son T
Assistant Examiner: Sinha; Tarun
Attorney, Agent or Firm: Haley Guiliano LLP
Parent Case Text
This application is a continuation of U.S. patent application Ser.
No. 14/064,019 filed on Oct. 25, 2013, which claims priority to,
and the benefit of, U.S. Provisional Application Nos. 61/719,332
and 61/719,339, each filed on Oct. 26, 2012, the entire contents of
which are hereby incorporated by reference.
Claims
What is claimed is:
1. A structural health monitoring system, comprising: first and
second bearings configured for rotatable positioning along a
structure; a spacer positioned between the first and second
bearings, the first and second bearings placed against opposing
sides of the spacer and having a preload force engaging the
respective first and second bearings against the opposing sides of
the spacer; and a plurality of sensors coupled to the spacer so as
to be positioned at an outer surface of the spacer between the
first and second bearings, and facing one of the first and second
bearings, the sensors further coupled to at least one of the first
and second bearings so as to be configured to monitor a structural
health of the at least one of the first and second bearings.
2. The structural health monitoring system of claim 1, wherein the
sensors are coupled to the at least one of the first and second
bearings so as to be able to generate stress waves in, and receive
stress waves from, the at least one of the first and second
bearings.
3. The structural health monitoring system of claim 2, wherein the
sensors are affixed to a side of the spacer so as to be positioned
between the first and second bearings.
4. The structural health monitoring system of claim 3, wherein the
sensors are positioned within one or more depressions in the
spacer.
5. The structural health monitoring system of claim 3, wherein the
side of the spacer is substantially planar, so that the sensors
protrude from the side of the spacer toward at the least one of the
first and second bearings.
6. The structural health monitoring system of claim 2, wherein the
sensors contact the at least one of the first and second
bearings.
7. The structural health monitoring system of claim 2, wherein the
sensors are embedded within the spacer.
8. The structural health monitoring system of claim 7, wherein the
spacer comprises a laminated composite material having a plurality
of layers, and wherein the sensors are embedded between the layers
of at least one pair of the layers.
9. The structural health monitoring system of claim 1, wherein the
sensors comprise piezoelectric polymer layers.
10. The structural health monitoring system of claim 1, wherein the
sensors are coupled to the at least one of the first and second
bearings so as to be able to measure a magnitude of the preload
force.
Description
BRIEF DESCRIPTION
This invention relates generally to structural health monitoring
(SHM). More specifically, this invention relates to systems and
methods for monitoring the structural health of coupled
bearings.
BACKGROUND
Coupled bearing elements have historically posed challenges to
structural health monitoring systems. As the individual bearings
are compressed together with a preload force, the space between the
bearings forms a challenging environment for SHM sensors. Little to
no room exists for sensors to be placed between bearings, and any
sensors placed there must be able to withstand the preload, and
other, forces.
SUMMARY
The invention can be implemented in a number of ways, such as by a
structural health monitoring system.
In one embodiment, a structural health monitoring system comprises
first and second bearings configured for rotatable positioning
along a structure, and a spacer positioned between the first and
second bearings. The first and second bearings are placed against
opposing sides of the spacer and have a preload force engaging the
respective first and second bearings against the opposing sides of
the spacer. A plurality of sensors is coupled to the spacer so as
to be positioned between the spacer and at least one of the first
and second bearings, the sensors further coupled to at least one of
the first and second bearings so as to be configured to monitor a
structural health of the at least one of the first and second
bearings.
The sensors may be coupled to the at least one of the first and
second bearings so as to be able to generate stress waves in, and
receive stress waves from, the at least one of the first and second
bearings.
The sensors may be affixed to a side of the spacer so as to be
positioned between the first and second bearings.
The sensors may be positioned within one or more depressions in the
spacer.
The side of the spacer may be substantially planar, so that the
sensors protrude from the side of the spacer toward at the least
one of the first and second bearings.
The sensors may contact the at least one of the first and second
bearings.
The sensors may be embedded within the spacer.
The spacer may comprise a laminated composite material having a
plurality of layers, wherein the sensors are embedded between the
layers of at least one pair of the layers.
The sensors may comprise piezoelectric polymer layers.
The sensors may be coupled to the at least one of the first and
second bearings so as to be able to measure a magnitude of the
preload force.
In another embodiment, a structural health monitoring system
comprises first and second bearings coupled to each other at least
partially by a preload force, and a plurality of sensors affixed to
at least one of the first and second bearings. The sensors are
positioned between the first and second bearings so as to be
configured to monitor a structural health of at least one of the
bearings.
The sensors may be coupled to the at least one of the first and
second bearings so as to be able to generate stress waves in, and
receive stress waves from, the at least one of the first and second
bearings.
This embodiment may further comprise a spacer positioned between
the first and second bearings, so that the sensors are positioned
between the spacer and at least one of the first and second
bearings. The sensors may contact the spacer.
The sensors may be coupled to the at least one of the first and
second bearings so as to be able to measure a magnitude of the
preload force.
The sensors may be positioned within one or more depressions in the
at least one of the first and second bearings.
The sensors may be affixed to one or more sides of the at least one
of the first and second bearings, wherein each side of the one or
more sides is substantially planar, so that the sensors protrude
from the each side.
Other aspects and advantages of the invention will become apparent
from the following detailed description taken in conjunction with
the accompanying drawings which illustrate, by way of example, the
principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention, reference should be
made to the following detailed description taken in conjunction
with the accompanying drawings, in which:
FIG. 1 is an exploded view of a coupled bearing assembly in
accordance with embodiments of the present invention.
FIG. 2 illustrates operation of coupled bearings of embodiments of
the present invention.
FIG. 3 is a block diagram representation of a system for monitoring
coupled bearing elements, according to embodiments of the present
invention.
FIGS. 4 and 5 conceptually illustrate the configuration of one
embodiment of the electrical interface unit of FIG. 3, implemented
on a rotating shaft.
FIGS. 6 and 7 are pictures of an actual implementation of one
system exemplifying an embodiment of the invention.
FIG. 8 illustrates a cross-section of an electrical interface unit,
that is taken along section I-I of FIG. 4.
FIG. 9 illustrates a plan view of the inner ring and portions of
the outer ring of the electrical interface unit of FIG. 4.
Like reference numerals refer to corresponding parts throughout the
drawings. The various Figures are not necessarily to scale.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
In one embodiment, the invention relates to the structural health
monitoring of coupled bearings. A number of sensors are placed
in-between a pair of bearings that have a compressive preload force
applied--a location that is difficult to monitor by conventional
means. The sensors can thus measure the preload force, as well as
the structural health of the bearings, during bearing operation.
This reduces bearing downtime, in addition to allowing for
real-time monitoring of bearing health during operation.
A system is provided for conducting structural health monitoring of
bearings, and in particular, coupled bearing assemblies. FIG. 3 is
a block diagram representation of an embodiment of an exemplary
such system, which includes an analyzer 10, interface unit 20,
cable 30, and sensor array 40. The sensor array 40 can be a
flexible substrate that contains any number of sensors 50, and may
or may not be present. That is, the sensors 50 may be present by
themselves, or they may be incorporated into an additional flexible
substrate.
FIG. 1 is an exploded view of a coupled bearing assembly in
accordance with embodiments of the present invention, and FIG. 2
illustrates operation of this coupled bearing assembly. Here, two
bearings 60 and 70 are placed along a screw shaft 100. In typical
such cases, the bearings 60, 70 contain ball bearings placed along
their threaded groove, and these ball bearings sit in corresponding
threads of the screw shaft to allow for actuation when the shaft is
turned. The bearings 60, 70 are typically preloaded against each
other, i.e. a compressive preload force pressing the bearings 60,
70 against each other is maintained, with a spacer 80 positioned
in-between the two and also being in compression.
The sensor array 40 (or simply the individual sensors 50) is placed
on the spacer 80 and faces one or both of the bearings 60, 70 so as
to be pressed against the bearings 60, 70 and to thereby be placed
in communication with the bearings 60, 70. In this manner, the
sensors 50 can transmit stress waves through their respective
bearings 60, 70 and also receive stress waves from them.
The sensors 50 can be any sensors capable of conducting structural
health monitoring analysis, but in one example can be known
piezoelectric sensors capable of both propagating ultrasonic guided
waves in the structure to which they are attached for active
querying thereof, as well as sensing stress waves in the part or
structure. In another example, the sensors 50 can include
polyvinylidene fluoride (PVDF) sensors, constructed from a
piezoelectric PVDF polymer layer. The sensors 50 can also include
other types of sensors that are capable of detecting static
pressure, such as that applied by the above referenced preload
force.
The sensors send/receive signals to/from analyzer 10 for analysis,
via the interface unit 20. The analyzer 10 can include both power
transmission capability for actuating sensors 50 during active
querying, as well as analysis capability for analyzing sensed
signals from the sensors 50 to determine the health of the
bearings. The interface unit 20 can be any unit that provides or
facilitates electrical or electronic communication between the
sensors 50 and analyzer 10. As one example, the interface unit 20
can be a wireless transceiver unit affixed to one or more of the
bearings 60, 70, and spacer 80. The transceiver unit can have a
known analog to digital converter (ADC, not shown) for converting
the analog electrical signals generated by the sensors 50 to
digital signals, and broadcasting these digital signals (perhaps
after filtering by one or more known signal filters, also not
shown) wirelessly to analyzer 10. In this manner, the bearings 60,
70 can undergo rotational and translational motion without the need
for wires or any other physical connection to the analyzer 10.
Similarly, the analyzer 10 can transmit digital waveforms to the
transceiver unit, whereupon the interface unit 20 converts them to
analog signals via a known digital to analog converter (DAC, not
shown), amplifies the analog signals via a known power source (not
shown), and transmits the amplified signals to the sensors 50. The
sensors 50 then generate corresponding stress waves in the bearings
60, 70 and/or spacer 80.
As another example, the interface unit 20 can be a ringlike
coupling placed on the shaft 100. The ringlike coupling has an
inner housing that is affixed to and rotates with the shaft 100, as
well as an outer housing that is electrically coupled to the inner
housing but is free to rotate with respect to the inner housing.
Brushes extend from the inner housing to contact the outer housing,
providing electrical connections between the sensors 50 and
electrical terminals on the outer housing. This ringlike coupling
is described in further detail below. It should be noted, however,
that both this ringlike coupling and the abovementioned wireless
transceiver are but two mechanisms for implementing electronic
communication between the sensors 50 and analyzer 10, and any other
mechanism providing for such electronic communication is also
contemplated. For example, the sensors 50 can simply be directly
connected to the analyzer 10 via a plurality of wires, although in
some applications these wires may undesirably interfere with
rotation of the bearings 60, 70.
The sensors 50 can each be separately bonded to the spacer 80.
Alternatively, the sensors 50 can be integrated into a flexible
dielectric layer (represented by sensor array 40 in FIG. 3), so
that only a single layer need be bonded to the rotating element.
Such layers and their arrays of sensors 50 are known, and are
further described in, for example, U.S. Pat. Nos. 7,413,919 and
6,370,964 which are both hereby incorporated by reference in their
entireties.
The sensors 50 may be bonded to either of the surfaces of spacer 80
that face bearings 60 and 70. That is, the spacer 80 may have
surfaces facing bearings 60, 70 (in FIG. 1, the leftmost and
rightmost surfaces of the spacer 80) that are substantially planar
surfaces as shown in FIG. 1, where the sensors 50 or their sensor
array 40 are bonded to either one or both of these surfaces.
The leftmost and rightmost surfaces of the spacer 80 of FIG. 1 may
also have one or more depressions machined in them (see, e.g., the
lighter-colored circular areas of spacer 80 in FIG. 1), where each
depression is sized to fit one or more sensors 50. The sensors 50
can be bonded to the spacer 80 within these depressions. The
depressions are machined to a depth that is less than or equal to
the height of a sensor 50, so that the top of each sensor 50 is
coplanar with the upper surface of the spacer 80 or extends
slightly above the upper surface (so as to be placed in slight
compression by the bearings 60, 70 when they are preloaded together
with the spacer 80 in-between). This allows the sensors 50 to
contact the bearing 60, 70 that it faces, so that it may generate
and/or detect stress waves within that bearing 60, 70.
Alternatively, the sensors 50 can be incorporated directly into the
spacer 80, such as by fabricating a composite or laminated spacer
80 having sensors 50 incorporated into the composite or laminate
layers. More specifically, the spacer 80 can be fabricated as a
composite laminate spacer in known fashion, with a number of layers
adhered to each other within a matrix, where the sensors 50 are
placed between layers so as to be affixed within the body of spacer
80. In this case, wires 30 would extend from each of the sensors 50
to the exterior of the spacer 80 to be connected to interface unit
20.
Still further, the sensors 50 can be affixed to one or more sides
of the bearings 60, 70 that face the spacer 80, rather than being
affixed to the spacer 80. In particular, the sensors 50 can be
bonded or otherwise affixed to one or more of the planar surfaces
of bearings 60, 70 which face spacer 80 in FIG. 1. In this manner,
the sensors 50 are placed in contact with a surface of the spacer
80 when the bearings 60, 70 are preloaded against the spacer 80.
Alternatively, pockets or depressions can be machined in the
surfaces of bearings 60, 70 which face the spacer 80, and the
sensors 50 can be placed in the pockets. In this case, the sensors
50 would protrude from the upper surface of the pocket slightly so
as to contact the spacer 80 or the opposite bearing 60, 70 (if the
spacer 80 is removed and the bearings 60, 70 are preloaded against
each other), so that the sensors 50 are capable of
generating/detecting stress waves in the spacer 80 or opposite
bearing 60, 70.
In this manner, embodiments of the invention allow for a network of
structural health monitoring sensors 50 to be directly coupled to a
bearing within its bearing assembly, so that the sensors 50 can
monitor the structural health of the bearing assembly during its
operation and in real time. In particular, the system can monitor
the preload force applied between the bearings 60, 70 to determine
any weakening in preload over time, and can also measure acoustic
signals generated by the ball bearings during their operation,
which as is known can indicate characteristics of wear in the ball
bearings.
The sensors 50 and analyzer 10 can also be configured to conduct
any other type of structural health monitoring. For example, the
sensors 50 can query the structure (or passively detect stress
waves generated during operation of the rotating part) for
detection of fatigue cracks, corrosion, plastic deformation in
metallic parts and delaminations, disbonds, and cracking in
composite part, and/or any other quantities of interest in
structural health monitoring.
In operation, the sensor array 40 can be affixed to the spacer 80
so that the sensors 50 face one of the bearings 60, 70. When the
bearings are preloaded against one another, the sensors 50 are
pressed against one of the bearings 60, 70, and can thus monitor
that bearing 60, 70 for various structural health quantities. In
particular, the sensors 50 can actively query the bearings 60, 70
by transmitting stress waves therethrough, and/or can passively
monitor the bearings 60, 70 for acoustic waves generated by the
bearings 60, 70, or any other quantities. If the sensors 50 are
simply attached to a surface of the spacer 80 facing the bearings
60, 70, the sensors 50 may be configured as PVDF sensors that can
withstand the compressive forces of the bearing preload and still
operate as described herein.
In another embodiment, the system uses piezoelectric discs to
propagate ultrasonic guided waves in the bearing assembly. The
piezoelectric discs can serve as actuators and sensors. The
piezoelectric discs can be embedded in a flexible polyimide film
which also contains the wiring for every disc. The polyimide film
containing the piezoelectric discs is bonded to one or more of the
spacer 80 and bearings 60, 70. The wiring in the polyimide film is
routed to a central area for a simple connection to the interface
unit 20.
It is desirable to maintain the correct pre-load in the bearing
during operation. As the bearing is used during operation, heat may
cause expansion which increases pre-load. As the bearings inside
the ball screw begin to wear, the pre-load decreases. If the
pre-load of the bearing could be continuously monitored, more
optimal operating conditions could be implemented. Thus, in other
embodiments, the sensors 50 can include force sensors (known and
including, but not limited to, the otherwise installed and utilized
piezoelectric sensors) to provide continuous feedback about the
operating conditions of the ball screw. Force sensors would be used
to monitor the pre-load, while the piezoelectric or PVDF sensor
would monitor the ball screw damage. The piezoelectric or PVDF
elements would be able to actuate or sense ultrasonic waves
enabling damage detection. In this manner, the system would be able
to detect fatigue cracks, corrosion, plastic deformation, and/or
other structural health quantities, while the force sensors would
be used to track the pre-load during operation and alert the
operator if a preload adjustment is needed. The systems of the
invention can include arrays of sensors 50 that include any
combination of force sensors, piezoelectric sensors, and any other
sensors as appropriate.
Ringlike Coupling
As described above, one nonlimiting exemplary embodiment of the
interface unit 20 can be a ringlike coupling with an inner housing
that is affixed to and rotates with the shaft 100, as well as an
outer housing that is electrically coupled to the inner housing but
is free to rotate with respect to the inner housing.
In this embodiment, interface unit 20 is configured to be coupled
to the rotating part (i.e. shaft 100), along with sensor array 40,
so that sensor array 40, cable 30, and at least a portion of
interface unit 20 each rotate with the rotating part. In one
embodiment, the interface unit 20 can be a slip ring with a
stationary outer housing and an inner housing rotationally coupled
to the outer housing. The inner housing is attached to the rotating
part and spins with the part, while the outer housing is fixed (or
at least does not move exactly along with the inner housing) and
contains electrical and electronic connections for communication
with analyzer 10. More specifically, the inner housing can contain
a number of interfaces to each of the sensors 50, so that the cable
30 maintains individual connections between each sensor 50 at one
end, and a corresponding interface at the other end. The interfaces
are each electrically connected to a separate conductive brush,
which is in turn positioned to contact a conductive ring in the
outer housing. Each ring is positioned so that as its brush spins,
it continuously contacts the ring, thus maintaining an electrical
contact between a particular sensor 50 and the ring. Each ring is
in turn electrically connected to one of the electrical connections
in the outer housing, i.e. is connected to the analyzer 10. In this
manner, each sensor 50 has its own separate electrical connection
to analyzer 10, through the interface unit 20. Further, each
electrical connection is insulated from the remaining electrical
connections, so that each sensor 50 can be individually controlled
by the analyzer 10.
FIGS. 4 and 5 conceptually illustrate the configuration of this
embodiment, implemented on a rotating shaft. The sensor array 40,
shown as being incorporated into or onto a flexible layer shaped
for affixing to the shaft 100, is bonded to the shaft 100. The
interface unit 20 is shown as a slip ring whose inner housing is
attached to the shaft 100.
FIGS. 8 and 9 illustrate further details of interface unit 20. FIG.
8 is a cross-sectional view of interface unit 20, and FIG. 9 is a
plan view of the inner ring thereof, as well as a portion of the
outer ring. More specifically, the slip ring or interface unit 20
has an inner ring 200 and outer ring 202. The inner ring 202 is
attached to shaft 100, and rotates therewith. The outer ring 202 is
positioned radially outward from the inner ring 200, and is free to
rotate independent of inner ring 200, or can be affixed so that it
does not rotate. Each of the inner ring 200 and outer ring 202 can
be made of any suitable material. For example, each can be made of
a steel or other metal that is compatible with the material of the
shaft 100.
The inner ring 200 has a number of conductive brushes 206 extending
radially outward therefrom, where each brush 206 is connected by
cable 30 and wiring 204 to one particular sensor 50. The conductive
brush 206 has a number of conductive bristles made of a metal or
other conductor, and extends radially outward to contact a
conductive collar 210 bonded to outer ring 202. The conductive
collar 210 is bonded to the outer ring 202 with an insulating
adhesive, or alternatively can have an insulating layer (not shown)
placed between itself and the outer ring 202 (or, the outer ring
202 can simply be made of an insulating material). Each conductive
collar 210 is electrically connected to a separate terminal 208 on
the exterior of outer ring 202, as shown. Leads from analyzer 10
can then be connected to each terminal 208 to transmit/receive
electrical signals to/from each sensor 50.
As can be seen from FIG. 9, each sensor 50 is connected to a
separate conductive brush 206 which in turn contacts, and is thus
electrically connected to, one of the conductive collars 210 of
outer ring 202. Thus, a continuous electrical pathway is maintained
between each sensor 50 and its associated terminal 208. As the
shaft 100 rotates about its major axis (and hence each sensor 50
rotates about the same axis), each brush 206 rotates in the same
manner, its bristles frictionally contacting its respective collar
210 and thus maintaining electrical contact therewith. In FIG. 9,
note that the collars 210 are connected to, and may be considered
part of, outer ring 202.
Embodiments of the invention are not limited to those shown. For
example, while the conductive brushes 206 are shown as attached to
the inner ring 200, one of ordinary skill in the art will observe
that the brushes 206 can instead be attached to the outer ring 202,
so that their bristles frictionally contact the inner ring 200. In
such a configuration, the inner ring 200 can have a number of
collars that are insulated from each other, where each brush 206
contacts one of these collars. Each collar is then placed in
electrical contact with one of the sensors 50.
FIGS. 6 and 7 are pictures of an actual implementation of one
system exemplifying an embodiment of the invention. Shown is a
metallic shaft that rotates, with a PCB-like flexible sensor array
layer bonded to the shaft. The flexible layer contains a number of
piezoelectric sensors that are thereby placed in communication with
the shaft. The slip ring can be seen in the background of FIG. 6,
and the sensor layer extends into the slip ring, for electrical
contact to the connections maintained in its inner housing.
The forgoing description, for purposes of explanation, used
specific nomenclature to provide a thorough understanding of the
invention. However, it will be apparent to one skilled in the art
that the specific details are not required in order to practice the
invention. Thus, the foregoing descriptions of specific embodiments
of the present invention are presented for purposes of illustration
and description. They are not intended to be exhaustive or to limit
the invention to the precise forms disclosed. Many modifications
and variations are possible in view of the above teachings. For
example, the sensors 50 can be arranged in any configuration and
number on the bearings, with each of the sensors 50 facing one
bearing 60, 70 or some facing one bearing 60, 70 and others facing
the other bearing 70, 60. Also, the sensors 50 can be incorporated
into a dielectric layer or individually placed. The sensors 50 can
be PVDF sensors, piezoelectric ceramic sensors, or any other type
of sensors, and can be affixed to a surface of the bearing or
spacer, in depressions machined therein, or can be incorporated
into the structure of the bearings and/or spacer. Also, the various
embodiments each have certain features that differ from those of
other embodiments, and it is noted that the invention contemplates
the mixing and matching of various features as desired. That is,
further embodiments can be formed from the selection of various
features from different embodiments. The embodiments were chosen
and described in order to best explain the principles of the
invention and its practical applications, to thereby enable others
skilled in the art to best utilize the invention and various
embodiments with various modifications as are suited to the
particular use contemplated.
* * * * *